A patent covering the polymer-stimulated ligation of DNA has been issued. Macromolecular crowding has been used to obtain efficient phosphorylation by T4 polynucleotide kinase of types of termini in duplex DNA -- such as termini at "nicks" or recessed termini -- which are otherwise only very slowly or incompletely labeled under conventional procedures. Macromolecular crowding was found to extend the range of ionic conditions which support high DNA polymerase reaction rates. High concentrations of nonspecific polymers increased polymerase activity under otherwise inhibitory conditions resulting from relatively high ionic strength. The primary mechanism of the polymer effect seems to be to increase the binding of polymerase to DNA. We have suggested that this effect on protein-DNA complexes is only one example of a general "metabolic buffering" action of crowded solutions on a variety of macromolecular interactions.